排序方式: 共有406条查询结果,搜索用时 265 毫秒
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Christopher E. Doughty Adam Wolf Naia Morueta‐Holme Peter M. Jørgensen Brody Sandel Cyrille Violle Brad Boyle Nathan J. B. Kraft Robert K. Peet Brian J. Enquist Jens‐Christian Svenning Stephen Blake Mauro Galetti 《Ecography》2016,39(2):194-203
During the Late Pleistocene and early Holocene 59 species of South American megafauna went extinct. Their extinction potentially triggered population declines of large‐seeded tree species dispersed by the large‐bodied frugivores with which they co‐evolved, a theory first proposed by Janzen and Martin (1982). We tested this hypothesis using species range maps for 257 South American tree species, comparing 63 species thought to be primarily distributed by megafauna with 194 distributed by other animals. We found a highly significant (p < 0.001) decreased mean range size of 26% for the megafauna dispersed fruit (n = 63 species) versus fruit dispersed by other animals (n = 194), results which support the hypothesis. We then developed a mathematical model of seed dispersal to estimate the theoretical impact of megafauna extinction on tree species range and found the estimated dispersal capacity (Φseed) of a 2 g seed decreases by > 95% following disperser extinction. A numerical gap dynamic simulations suggests that over a 10 000 yr period following the disperser extinctions, the average convex hull range size of large‐seeded tree species decreased by ~ 31%, while the estimated decrease in population size was ~ 54%, indicating a likely greater decrease in species population size than indicated by the empirical range patterns. Finally, we found a positive correlation between seed size and wood density of animal‐dispersed tree species implying that the Late Pleistocene and early Holocene megafaunal extinctions reduced carbon content in the Amazon by ~ 1.5 ± 0.7%. In conclusion, we 1) provide some empirical evidence that megafauna distributed fruit species have a smaller mean range size than wind, water or other animal‐dispersed species, 2) demonstrate mathematically that such range reductions are expected from megafauna extinctions ca 12 000 yr ago, and 3) illustrate that these extinctions may have reduced the Amazon's carbon storage capacity. 相似文献
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Naia Morueta‐Holme Benjamin Blonder Brody Sandel Brian J. McGill Robert K. Peet Jeffrey E. Ott Cyrille Violle Brian J. Enquist Peter M. Jørgensen Jens‐Christian Svenning 《Ecography》2016,39(12):1139-1150
Positive and negative associations between species are a key outcome of community assembly from regional species pools. These associations are difficult to detect and can be caused by a range of processes such as species interactions, local environmental constraints and dispersal. We integrate new ideas around species distribution modeling, covariance matrix estimation, and network analysis to provide an approach to inferring non‐random species associations from local‐ and regional‐scale occurrence data. Specifically, we provide a novel framework for identifying species associations that overcomes three challenges: 1) correcting for indirect effects from other species, 2) avoiding spurious associations driven by regional‐scale distributions, and 3) describing these associations in a multi‐species context. We highlight a range of research questions and analyses that this framework is able to address. We show that the approach is statistically robust using simulated data. In addition, we present an empirical analysis of > 1000 North American tree communities that gives evidence for weak positive associations among small groups of species. Finally, we discuss several possible extensions for identifying drivers of associations, predicting community assembly, and better linking biogeography and community ecology. 相似文献
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Luana Alves Rodrigues Eduardo Augusto Ruas Paulo Maurício Ruas Maikel Reck Fernando Gianetti Fiorin María Ángeles Ortiz Estrella Urtubey Nelson Ivo Matzenbacher Claudete Fátima Ruas 《Plant Species Biology》2016,31(1):55-64
The genus Hypochaeris has a recent evolutionary history caused by long‐distance dispersal in conjunction with adaptive radiation in the South American continent. Hypochaeris lutea is a perennial herb that grows mostly at altitudes of around 1000 m in cold swamps of the southern regions of Brazil. We investigated the amplified fragment length polymorphism (AFLP) in 270 individuals representing 11 Brazilian populations of H. lutea to elucidate the population genetic structure of this species. The frequencies of polymorphic loci and gene diversity ranged from 83.42% to 91.66% and from 0.26 to 0.34, respectively. Analysis of molecular variance revealed that most of the genetic variability was found within (76.67%) rather than among (23.3%) populations, agreeing with the pattern of genetic distribution within and among populations observed in other allogamous species of Hypochaeris. A Mantel test showed no correlation between genetic and geographic distances when all populations were considered. Simulations performed using a Bayesian approach consistently identified two clusters with different admixture proportions of individuals, as also revealed by a UPGMA dendrogram of populations. The pattern of genetic structure observed in H. lutea is consistent with a process of successive colonization events by long‐distance dispersal resembling the rapid and recent radiation that has been proposed to explain the origin of the South American species of Hypochaeris. 相似文献
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Luana Lugini Cristina Federici Martina Borghi Tommaso Azzarito Maria Lucia Marino Albino Cesolini 《Journal of enzyme inhibition and medicinal chemistry》2016,31(4):538-545
Context: Tumor acidity represents a major cause of chemoresistance. Proton pump inhibitors (PPIs) can neutralize tumor acidity, sensitizing cancer cells to chemotherapy.Objective: To compare the anti-tumor efficacy of different PPIs in vitro and in vivo.Materials and methods: In vitro experiments PPIs anti-tumor efficacy in terms of cell proliferation and cell death/apoptosis/necrosis evaluation were performed. In vivo PPIs efficacy experiments were carried out using melanoma xenograft model in SCID mice.Results: Lansoprazole showed higher anti-tumor effect when compared to the other PPIs. The lansoprazole effect lasted even upon drug removal from the cell culture medium and it was independent from the lipophilicity of the PPIs formulation.Discussion: These PPIs have shown different anti-tumoral efficacy, and the most effective at low dose was lansoprazole.Conclusion: The possibility to contrast tumor acidity by off-label using PPIs opens a new field of oncology investigation. 相似文献
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Luana P. Gonçalves Tainã F. O. Alves Cristina P. S. Martins Aurizangela O. de Sousa Ivanildes C. dos Santos Carlos P. Pirovani Alex-Alan F. Almeida Mauricio A. Coelho Filho Abelmon S. Gesteira Walter dos S. Soares Filho Eduardo A. Girardi Marcio G. C. Costa 《Acta Physiologiae Plantarum》2016,38(7):174
The poorly understood physiological and biochemical drought responses induced in sweet orange by citrus rootstocks of contrasting drought tolerance were investigated during a drought/rewatering cycle under controlled conditions. Long-term exposure of the grafted trees to a gradually increasing water deficit and subsequent recovery revealed distinct strategies of drought acclimation that were induced by the different rootstocks. Trees grafted onto the drought-tolerant rootstock ‘Cravo’ rangpur lime were less water conservative, exhibiting an increased cell-wall elasticity that contributes to turgor maintenance and its related processes of growth and photosynthesis over a wider range of soil–water potentials. On the other hand, the drought-tolerant ‘Sunki Tropical’ mandarin and drought-sensitive ‘Flying Dragon’ trifoliate orange rootstocks induced a water conservation strategy by increasing tissue rigidity under drought. ‘Sunki Tropical’ was also able to induce osmotic adjustment, conferring thereby a more efficient water conservation strategy than ‘Flying Dragon’ by allowing for turgor maintenance at lower soil–water potentials while attenuating cell dehydration and shrinkage. In contrast to ‘Cravo’ and ‘Sunki Tropical’, trees grafted onto ‘Flying Dragon’ exhibited a significant photoinhibition of the photosystem II reaction centers, as well as an increased H2O2 production and lipid peroxidation under drought treatment. A significantly higher activity of the antioxidant enzyme GPX was also observed in drought stressed trees grafted onto ‘Flying Dragon’. Collectively, these results support the involvement of elastic and osmotic adjustments, as well as the control of oxidative stress, as functional leaf traits associated with the rootstock-induced drought tolerance in sweet orange. 相似文献
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Markus Egli Simon Hafner Curdin Derungs Judith Ascher-Jenull Federica Camin Giacomo Sartori Gerald Raab Luana Bontempo Mauro Paolini Luca Ziller Tommaso Bardelli Marta Petrillo Samuel Abiven 《Biogeochemistry》2016,131(3):321-338
Only scarce information is available on how organic C is incorporated into the soil during the decay and how (micro) climate influences this process. Therefore, we investigated the effect of exposure and elevation on the organic litter decomposition and C-stabilisation in acidic soils of an Alpine environment. An experiment with artificially 13C labelled Norway spruce needles was carried out at north- and south-exposed sites between 1200 and 2400 m a.s.l. in the Italian Alps using mesocosms. After 1 year, the 13C recoveries of the bulk soil were 18.6% at the north-facing slopes and 31.5% at the south-facing slopes. A density fractionation into a light (LF; ≤1.6 g cm?3) and a heavy fraction (HF; >1.6 g cm?3) of the soil helped to identify how the applied substrate was stabilised. At the northern slope, 10.5% of the substrate was recovered in the LF and 8.1% in the HF and at the south-facing slope 22.8% in the LF and 8.1% in the HF. The overall 13C recovery was higher at the south-facing sites due to restricted water availability. Although the climate is humid in the whole area, soil moisture availability becomes more important at south-facing sites due to higher evapotranspiration. However, at sites >1700 m a.s.l, the situation changed, as the northern slope had higher recovery rates. At such altitudes, temperature effects are more dominant. This highlights the importance of locally strongly varying edaphic factors when investigating the carbon cycle. 相似文献
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Priscila L. dos Santos Fabrícia A. de Oliveira Micheli Luize B. Santos Luana Celina S. Cunha Michelle T. B. Lino Michelle F. S. de Oliveira Manuela O. M. Bomfim Angela Maria Silva Tatiana R. de Moura Amélia R. de Jesus Malcolm S. Duthie Steven G. Reed Roque P. de Almeida 《PLoS neglected tropical diseases》2016,10(1)